FIELD OF THE INVENTION
The present invention relates to a thermal compression bonding method of an electronic part with a solder bump for thermal compression bonding of an electronic part with a solder bump such as a flip chip and the like to a circuit board.
There has been known a method by a thermal compression bonding as a method of mounting an electronic part with a solder bump such as a flip chip and the like to a circuit board. The method is constituted by pressing the electronic part to the circuit board by a thermal compression bonding tool, heating the electronic part so as to melt the solder bump in the electronic part, and soldering to an electrode of the circuit board. In this thermal compression bonding process, when the solder bump is brought into contact with the electrode, the solder bump is at a temperature equal to or less than a melting point of the solder, and the solder bump is melted when a certain time passes after the solder bump is brought into contact.
After the solder bump is melted, it is performed to extend the melted solder to a predetermined height by slightly ascending a thermal compression bonding tool holding the electronic part. A timing of ascending the thermal compression bonding tool has been conventionally set by a timer by supposing a time required for melting the solder bump. However, in the case of setting by the timer, since the melting of the solder bump is not actually confirmed, the melting time of the solder bump is set to be a little longer so that a complete melting is secured in all the cases. Accordingly, in almost cases, in spite that the solder bump is melted before the set timing, there is generated a useless time that the thermal compression bonding tool does not ascend immediately after melting, but stands by as it is, so that there has been a problem of preventing a productivity from being improved.
Further, in this thermal compression bonding step, when the pressing is continued after the solder bump is melted, the melted solder is crushed by the thermal compression bonding tool. Accordingly, the solder bump is prevented from being crushed by fixing a height position of the thermal compression bonding tool before the solder bump is melted. However, even in a state where the height position of the thermal compression bonding tool is fixed, the thermal compression bonding tool presses the electronic part to the circuit board under a certain pressing load, and an elastic strain corresponding to the pressing load is generated in a pressing mechanism of a thermal compression bonding apparatus which receives a reaction force of the pressing load. Accordingly, at the same time when the solder bump is melted and the pressing load applied to the solder bump disappears, the elastic strain is released, so that the thermal compression bonding tool is displaced downward at a degree corresponding to the elastic strain of the pressing mechanism. In the case that an amount of this displacement is large, there is a case of crushing the melted solder bump. Therefore, there has been a problem that a disadvantage such as a bridge, that is, connection to an adjacent bump is generated in some cases.